Abstract
PurposeOur study aimed to explore the feasibility of manganese‐enhanced magnetic resonance imaging (MEMRI) combined with visual evoked potentials (VEP) and auditory evoked visual cortex responses (AVR) in evaluating for the establishment of visual/auditory compensatory pathways after monocular blindness.Materials and MethodsA total of 14 healthy neonatal male Sprague‐Dawley rats were randomly divided into two groups (n = 7 for Groups A and B). Right optic nerve (ON) transection was performed on the 7 rats of Group A to obtain a monocularly blind model, and the 7 rats of Group B were chosen as the control group. Four months later, 400 mmol MnCl2 was injected into the left eye in both groups via intravitreal injection. The changes in the visual pathways projected from the blind eye and the remaining eye in Group A and the normal eyes in Group B were compared to determine if new visual compensatory pathways were established. Additionally, VEP tests were performed to determine complete blindness, and AVR examinations were performed to help identify the generation of auditory compensatory function.ResultsThe VEP test indicated complete visual loss after ON transection. In the monocularly blind rats, the contrast‐to‐noise ratio (CNR) of ON, optic tract (OT), lateral geniculate nucleus (LGN), superior colliculus (SC), optic radiation (OR) and visual cortex (VC) of visual pathway projected from the left eye was significantly higher than that of the right pathway (p < .001). Moreover, the CNR of ON, OT, LGN, SC, OR and VC in the visual pathway projected from the left eye of monocularly blind rats was significantly lower than those of normal rats (p < .05). The AVR results revealed that the corresponding bilateral visual cortex in monocularly blind rats did not respond to the auditory stimulus or showed dissimilation with the low frequency.Conclusion MEMRI combined with electrophysiology, including VEP and AVR, may be potentially helpful in the evaluation of the possible generation of new visual/auditory compensatory pathways after monocular blindness.
Highlights
Because of the increasing number of monocularly blind patients with total loss of optic nerve function caused by glaucoma and other diseases (Cumberland & Rahi, 2016; Rizzo et al, 2017), it is important to explore whether the structures of the central visual system have irreversible changes; this information is closely related to the feasibility of artificial vision (Marchini et al, 2016) and gene therapy (Ashtari et al, 2015), as well as the choice of therapeutic target (Cumberland & Rahi, 2016)
Many studies have used numerous advanced technologies to investigate the changes in the visual pathway after monocular blindness, such as blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI), visual evoked potentials (VEP), horseradish peroxidase (HRP) and other techniques (Chow et al, 2011; Dietrich, Hertrich, & Ackermann, 2015; Jeffery & Thompson, 1986; Mastropasqua et al, 2015; Qu, Dong, Sugioka, & Yamadori, 1996; Toldi, Feher, & Wolff, 1996)
There is an increasing number of studies on the changes in the visual cortex caused by monocular visual plasticity that use advanced technologies such as BOLD-fMRI, VEP, and HRP
Summary
Because of the increasing number of monocularly blind patients with total loss of optic nerve function caused by glaucoma and other diseases (Cumberland & Rahi, 2016; Rizzo et al, 2017), it is important to explore whether the structures of the central visual system have irreversible changes; this information is closely related to the feasibility of artificial vision (Marchini et al, 2016) and gene therapy (Ashtari et al, 2015), as well as the choice of therapeutic target (Cumberland & Rahi, 2016). The changes of signal intensity in the bilateral optic tracts, optic radiations and visual cortices of monocularly blind models have not been studied in depth
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